Over the past decade it has become abundantly clear that the highly prevalent C677T polymorphism of the methylenetetrahydrofolate reductase (MTHFR) gene imparts substantial protection against the risk of developing colorectal cancer, and that its effect in this regard is a function of a nutrient-gene interaction with the B-vitamin, folate. Individuals who are homozygous for the variant and who are folate-replete enjoy a reduction in risk of 30-70% compared to wild-type individuals with comparable levels of folate, with diminishing degrees of protection among those whose folate status is less robust. Far less appreciated are the observations from both pre-clinical and clinical studies that indicate that the homozygote possesses an elevated risk when folate status is low. This bipolar effect of the C677T variant, whereby it conveys protection when folate status is adequate but conveys risk when folate status is low, is unique amongst all polymorphisms that play a role in determining cancer risk. Recent studies by my laboratory implicate the Wnt signaling pathway as playing a large role in the modulation of carcinogenesis mediated by folate and the other 1-carbon micronutrients. The purpose of the proposed animal studies is to conduct the initial steps necessary to define the mechanistic basis for this bipolar effect of the C677T variant. Unraveling the mechanistic basis of this effect will serve very important basic and applied functions. First, understanding the basis of the folate-C677T interaction will contribute critical insights into the related, but not identical, issue of how folate availability modulates colorectal cancer risk. From a public health perspective, a thorough appreciation for the underlying principles of how folate and this polymorphism conspire to modulate carcinogenesis is absolutely essential if industrialized societies are to intelligently and safely implement folic acid fortification programs, as well as identify appropriate individuals to target for supplementation programs that can reduce the burden of cancer. To accomplish these goals, two experiments will be conducted that collectively utilize three genetically- engineered strains of mice: one strain that is predisposed to intestinal carcinogenesis (Apc1638N);one strain that displays activity through the Wnt signaling cascade (BAT/lacZ);and one strain containing a cre-lox conditional knockout of the MTHFR gene that we recently created ourselves that models the human homozygous variant. The first experiment will determine whether the MTHFR knockout modulates early stages of colorectal carcinogenesis in a bipolar fashion depending on 1-carbon nutrient status, thereby establishing the relevance of this model to the human. The second experiment will then identify whether the nutrient-gene interaction modulates the Wnt pathway and its downstream effects on the cell cycle in a fashion that recapitulates its effects on carcinogenesis. PUBLIC HEALTH RELEVANCE: The purpose of the proposed animal studies is to define the mechanistic basis for the interaction between the common genetic variant, C677T, and the availability of folate and other related B-vitamins in determining the risk of colon cancer. Unraveling the mechanistic basis of this effect will serve very important basic and applied functions. First, understanding the basis of the folate-C677T interaction will contribute critical insights into the related, but not identical, issue of how folate availability modulates colorectal cancer risk. From a public health perspective, a thorough appreciation for the underlying principles of how folate and this polymorphism conspire to modulate carcinogenesis is absolutely essential if industrialized societies are to intelligently and safely implement folic acid fortification programs, as well as identify appropriate individuals to target for supplementation programs that can reduce the burden of cancer.